1. Field of the Invention
The present invention relates to a connected device to be connected to an IEEE (Institute of Electrical and Electronics Engineers) 1394 serial bus (hereafter some times referred to simply as “bus”) in network, and more particularly to a technology to reduce the amount of used bandwidth in the entire network.
2. Description of the Related Art
A conventional connected device on a bus needs to acquire network resources, i.e. channel and bandwidth, from an IRM (Isochronous Resource Manager) for sending and receiving isochronous data to and from a further or other devices on the IEEE 1394 serial bus. An IRM is a connected device to manage resources on the bus such as channel and bandwidth. Here, the term “channel” is used to mean a path to pass isochronous data between a sender device and at least one receiver device, while the term “bandwidth” is used to mean bandwidth amount (time) of isochronous communication which is proportional to the size of a packet transmitted on one channel, and is inversely proportional to the transmission speed. Both channel and bandwidth are managed by BANDWIDTH_AVAILABLE (register) (refer to reference numeral 52 in FIG. 2) mapped in a register space.
When one connected device on the bus attempts to establish a new logical connection for sending and receiving isochronous data to and from a further connected device, there may be a case where a bandwidth on the bus is already used for an existing logical connection without leaving a sufficient bandwidth required by the one connected device for the new logical connection. In this case, there is no other way than that the one connected device waits until the bandwidth used for the existing logical connection is released for the new logical connection, if no countermeasure is taken. However, the bandwidth is inversely proportional to the transmission speed as described above. Thus, by changing a physical connection between the then connected devices on the bus, it may be possible to increase the maximum transmission speed at the link-layer level in the then existing and established logical connection, so as to reduce the amount of used bandwidth required for the existing logical connection. If the amount of used bandwidth is reduced, then it may be possible to acquire a bandwidth required for the new logical connection before or without the release of the bandwidth used for the existing and established logical connection.